Insulating dropped soffit in bedroom
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What is the best way to insulate a dropped soffit in a second floor bedroom?
Should I just let the blown-in insulation in the attic fill the cavity? I’ve had some advice to use rigid foam board to cap off the dropped soffit to bring it back into the thermal envelope of the home.
Does anything need to be done about air sealing the soffit?
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Replies
If your air barrier is the interior drywall, then the foam board over the top doesn't really accomplish much. Assuming you're insulating with loose-fill (blown) insulation on the attic floor, then yes, you could let it just fill that soffit, but I'd be a bit concerned about the increased depth of insulation exceeding the allowable weight for the drywall in the soffit area to support. The easiest way to deal with this is probably to run some cheap panel product (maybe 7/16" OSB) over the top of the soffit to support the insulation. You won't need to worry about air sealing that if your drywall is the air barrier, the OSB in this case would just be there to support the insulation above and to keep that weight off of the drywall under the soffit.
If you have DUCTWORK in that soffit, then I would want the air barrier to go up over the top of the soffit so that the ductwork would be fully within the building envelope. You could still use cheap panel products over the top, but you'd need to seal them into the rest of your air barrier on either side, and on the ends, of the soffit.
Bill